Olefin oxides have been used for various utilities in chemical industries. For example, olefin oxides have been used as intermediates for producing urethanes, glycol solvents, coating compositions, molding materials, surface active agents, plasticizers, and other products, and they have been produced by various processes.
Typical conventional processes for producing olefin oxides by epoxidation of olefins include the following three processes. The first process is a so-called "chlorohydrin process" and comprises reacting an olefin with chlorine or sodium hypochlorite in an alkaline medium to form chlorohydrin and subjecting chlorohydrin to dehydrochlorination to obtain an epoxide. The second process comprises air-oxidizing a hydrocarbon to form a hydroperoxide and epoxidizing an olefin with the hydroperoxide in the presence of a catalyst. This second process has a problem that a large amount of an alcohol is formed as a by-product from the hydroperoxide. The third process comprises air-oxidizing acetaldehyde to form peracetic acid, and epoxidizing an olefin with the peracetic acid. The third process also has a problem that a large amount of acetic acid formed as a by-product should be recovered.
In recent years, epoxidation of olefins by hydrogen peroxide has been proposed, and there are many reports on a process for producing olefin oxides which comprises reacting an olefin with hydrogen peroxide in an organic solvent in the presence of various types of epoxidation catalysts. The epoxidation catalysts used in these reports are mainly molybdenum and tungsten catalysts. These catalysts have a high catalytic activity, but they have a problem that they easily decompose hydrogen peroxide. Boron and arsenic catalysts have also been reported as catalysts having an epoxidation ability without causing such decomposition of hydrogen peroxide. However, the boron catalysts generally have a relatively low catalytic activity and the arsenic catalysts have a disadvantage in view of their high toxicity even though they have a relatively high catalytic activity, and, therefore, these catalysts are not satisfactory for practical use in industry.
Further, a process for epoxidation using a catalyst comprising an antimony compound and molybdenum or tungsten (Japanese Patent Publication No. 19216/80), or an organotin compound and molybdenum or tungsten (Japanese Patent Publication Nos. 25046/72 and 25323/72) has been proposed. Such catalyst has a relatively high catalytic activity, but it is still unsatisfactory in its low selectivity and reaction efficiency of hydrogen peroxide. As a result of extensive studies on epoxidation of olefins in the light of the above conventional disadvantages, the present inventors found catalysts comprising an antimony compound or an organotin compound having a high activity and a high selectivity and reached the present invention.